Let \(P_{tr}\)  be the probability that there is at least one device doing the transmission for a certain time. According to [1]}, it can be shown as
\({P_{tr}} = 1 - \prod \limits _{h = 1}^N {(\sum \limits _{n = 0}^\infty {{f_h}(n)} {{(1 - {\tau _h})}^n})}.\) 
